1. Field of the Invention
This invention relates to a rotary head type reproducing apparatus and more particularly to an apparatus for reproducing a recorded signal through the tracing of many recording tracks formed on a record bearing medium at a predetermined pitch, one after another. The reproducing rotary head is shifted by shifting means in a direction which crosses the rotation plane thereof.
2. Description of the Prior Art
In order to have a sharp image stably reproduced by so-called special reproduction carried out at an arbitrary tape travel speed which differs from the recording speed, (i.e. a high speed reproduction, low speed reproducing (including a still picture reproduction), backward or reverse rotating reproduction, etc. with a rotary head type reproducing apparatus such as a video tape recorder (hereinafter called a VTR)) the reproducing head of the apparatus must accurately trace each recording track for each scanning field to prevent the occurrence of a noise bar.
To meet this requirement, there has been known a method in which a pattern signal generating device generates a pattern signal corresponding to a distance from the reproducing head scanning locus obtained at an arbitrary tape travel speed to a recording track on the tape; and head shifting means such as a piezoelectric conversion element (a bimorph element, for example) shifts the position of the reproducing head in a direction perpendicular to the rotating plane thereof, according to the pattern signal obtained from the pattern signal generating device.
The conventional VTR employing the above-stated method is arranged as shown in FIG. 1 of the accompanying drawings. Referring to FIG. 1 which schematically shows only the arrangement of parts essentially related to the present invention, reference numeral 1 identifies a magnetic tape employed as a record bearing medium. The VTR is provided with reproducing heads 2A and 2B which have the same azimuth angle and are opposed to each other at an angle of 180 degrees. The heads 2A and 2B are mounted respectively on the free ends of piezoelectric conversion elements 3A and 3B, such as bimorph elements employed as the shifting means. The piezoelectric conversion elements 3A and 3B are mounted at their tail ends on a rotating member 4. The rotating member 4 is rotated by a head rotating motor 5 in the direction of the arrow shown in the drawing. Although it is not shown in the drawing, the heads 2A and 2B are rotated while protruding from a slit provided between a pair of tape guide drums in a manner which is well known. The tape 1 is obliquely wound at least 180 degrees arund the pair of drums. A rotation phase detector 6 detects the rotation phase of the heads 2A and 2B. A signal produced from the phase detector 6 is used as a head switching signal (hereinafter called the HSW signal) and is supplied to a head motor control circuit 7. The control circuit 7 controls, via a head motor driving circuit 8, the head motor 5, rotating the heads 2A and 2B at a predetermined phase and rotational frequency on the basis of the output of the detector 6. A control signal reproducing fixed head 9 (hereinafter called the CTL head) reproduces a control signal (hereinafter called the CTL signal), which is recorded in the lower part of the tape 1, at intervals of one frame portion in the longitudinal direction thereof. A capstan 10 moves the tape 1 in the longitudinal direction thereof in conjunction with a pinch roller (not shown). A capstan motor 11 rotates the capstan 10. A frequency signal generator 12 produces a frequency signal (hereinafter called the capstan FG signal or the first pulse signal), which corresponds to the rotation of the capstan 10. A capstan motor control circuit 13 controls the capstan motor 11 via a capstan motor driving circuit 14, rotating the capstan 10 at a predetermined phase and rotational frequency according to the CTL signal from the CTL head 9 and the capstan FG signal from the frequency signal generator 12. A pattern signal generating circuit 15 produces a pattern signal for the piezoelectric conversion elements 3A and 3B, having the heads 2A and 2B respectively trace one recording track on the tape 1 for each scanning field on the basis of the HSW signal from the rotation phase detector 6, the CTL signal from the CTL head 9 and the capstan FG signal from the frequency signal generator 12 in the event that reproduction is made at an arbitrary tape speed (including still picture reproduction and reverse rotating reproduction). A conversion element driving circuit 16 drives the conversion elements 3A and 3B according to the pattern signal produced from the pattern signal generating circuit 15.
FIG. 2 of the accompanying drawings shows an example of an arrangement of the above-stated pattern signal generating circuit 15. In this example, input terminals 17, 18 and 19 receive respectively the capstan FG signal from the frequency signal generator 12, the CTL signal from the CTL head 9 and the HSW signal from the rotation phase detector 6. A binary counter 20 counts the capstan FG signal coming from the terminal 17 and to be reset by the CTL signal coming from the terminal 18. A timing signal generating circuit 21 receives the HSW signal from the terminal 19 and generates a timing signal which is synchronized with the HSW signal. A presettable binary counter 22, which is preset by the timing signal of the timing signal generating circuit 21 with the output of the counter 20, is preset there as a preset datum PD and counts the capstan FG signal coming from the terminal 17. A digital-to-analog (hereinafter called D/A) converter 23 D/A converts the output of the counter 22 and produces a first pattern signal. Reference numeral 25 identifies an adder An output terminal 26 produces a conversion element controlling pattern signal (or a driving signal) which is produced from the adder 25. An oscillator 27 generates clock pulses of a predetermined frequency. A counter 28 counts the clock pulses generated by the oscillator 27 and to be reset by the timing signal produced from the timing signal generating circuit 21. Another D/A converter 29 D/A converts the output of the counter 28. The output of the counter 22 relates to a record bearing medium (or tape) moving speed while that of the other counter 28 is not relative to the tape 1 moving speed. The D/A converter 29 thus produces a fixed pattern signal (or a second pattern signal) for still picture reproduction.
Referring to FIGS. 3(a) to 3(g) an 4(A) and 4(B), the following description deals with the special reproducing operations of the VTR described above, emphasizing the operation of the pattern signal generating circuit 15 of FIG. 2.
FIGS. 3(a) to 3(g) jointly form a timing chart showing the ideal wave forms of outputs of the various parts shown in FIG. 2. Among these figures, FIGS. 3(d) to 3(g) show respectively the output wave forms obtained in the event of 1.5 times increased speed reproduction including the CTL signal, the output of the counter 20 of FIG. 2, the output of the presettable counter 22 (or the D/A converter 23) of FIG. 2 and the output of the adder 25. The timing chart of FIGS. 3(a) to 3(g) shows ideal outputs assuming that the frequency of the capstan FG signal is extremely high. FIGS. 4(A) and 4(B), respectively, show the relations of the loci of the scanning centers of the heads 2A and 2B to the loci of the center of the recording tracks on the tape 1 obtained in the event of still picture reproduction and 1.5 times increased speed reproduction.
First, with the heads 2A and 2B rotated by the head motor 5, the rotation phase detector 6 produces the HSW signal which is as shown in FIG. 3(a). Then, the timing signal generating circuit 21 included in the pattern signal generating circuit 15 shown in FIG. 2 produces the timing signal which is synchronized with the rise and fall of the HSW signal, as shown in FIG. 3(b). The D/A converter 29 produces a still pattern signal as shown in FIG. 3(c) shifting the heads 2A and 2B continuously a number of degrees corresponding to a 0 to 1 track pitch (hereinafter called TP) within a one field scanning range. When a so-called field still picture reproducing operation is to be performed, by reproducing alternately with the two heads 2A and 2B a field signal recorded in one recording track by a recording head of the same azimuth angle as that of the reproducing heads 2A and 2B, the relations of the loci of the scanning centers of the heads 2A and 2B to the recording track on the tape 1 become as shown in FIG. 4(A). In FIG. 4(A), full lines represent the center loci "a"]of recording tracks of a field signal recorded by a recording head having the same azimuth angle as the heads 2A and 2B. Broken lines represent the center loci "b" of a field signal recorded by a recording head having a different azimuth angle from that of the heads 2A and 2B. A double line arrow represents the center locus "c" of a scanning performed by the heads 2A and 2B. Reference symbol CTL identifies the recording loci of the CTL signal (in FIG. 4(B) also). As shown, the scanning center locus "c" of the heads 2A and 2B (hereinafter called the head locus) becomes a line segment diagonally connecting the starting end of the center locus "a" of the track to be reproduced (hereinafter called the track locus) with the terminating end of the locus of an adjacent track on the left-hand side. It is necessary to adjust the head locus "c" to the track locus "a" for correcting this deviation. For this adjustment, assuming that the traveling direction of the tape 1 for recording is "+" and a reverse direction thereto is "-", the heads 2A and 2B must be continuously shifted a number of degrees corresponding to track pitch values from 0 to -1 TP within a one field scanning range. Therefore, with the D/A converter 29 of FIG. 2 converting the output of the counter 28 into a still pattern signal as shown in FIG. 3(c), the heads 2A and 2B can be satisfactorily shifted for still picture reproduction.
The capstan FG signal produced from the frequency signal generator 12 accordingly, as the capstan 10 is rotated the capstan motor 11, is supplied to the counters 20 and 22, which are included in the pattern signal generating circuit 15 shown in FIG. 2. The counters 20 and 22 count the pulses of the capstan FG signal. Then, since the counter 20 is reset by the CTL signal coming from the CTL head 9 for every frame portion of the tape 1, the upper limit of the count output of the counter 20 corresponds to +2 track pitches (TP). In the event of 1.5 times increased speed reproduction, since the CTL signal becomes as shown in FIG. 3(d), the count output of the counter 20 becomes as shown in FIG. 3(e). For the adder 25, the presettable counter 22 counts the pulses of the capstan FG signal while having the above-stated output of the counter 20 preset at that location by the timing signal (FIG. 3(b)) from the timing signal generating circuit 21 at every point in time when the timing signal is produced. Therefore, the count output of the counter 22, i.e. the output of the D/A converter 23, becomes as shown in FIG. 3(f) in the event of 1.5 times increased speed reproduction. Accordingly, the adder 25 adds the output of the D/A converter 23 and that of the still pattern generator 24 obtained at the above-stated point of time, together. As a result, the adder 25 produces a pattern signal as shown in FIG. 3(g).
In the case of 1.5 times increased speed reproduction, the head locus of the heads 2A and 2B in relation to the track locus on the tape 1 becomes as shown in FIG. 4(B). In FIG. 4(B), reference symbols A1, A2, A3, ---identify head loci of the head 2A; B1, B2, B3, --- those of the head 2B; and a1, a2, a3, --- track loci of the field tracks recorded by a recording head of the same azimuth angle as that of the heads 2A and 2B. For a first field, the head 2A must be continuously shifted to a degree corresponding to track pitch values from 0 to +0.5 TP within the first field scanning range in order to adjust the head locus A1 to the track locus a1. For a second field, the head 2B must be continuously shifted to a degree from +1.5 TP to +2 TP within the second field scanning range in order to adjust the head locus B1 to the track locus a1. For a third field, the head locus A2 must be adjusted to the next track locus a2 by continuously shifting the head 2A to a degree from +1 TP to +1.5 TP within the third field scanning range. For a fourth field, the head locus B2 must be adjusted to the track locus a3 by continuously shifting the head 2B to a degree from +0.5 TP to +1 TP within the fourth field scanning range. It will be understood that the pattern signal of FIG. 3(g) is adequate for shifting the heads 2A and 2B in the above-stated manner.
In the foregoing, the pattern signal of the conventional apparatus for a 1.5 times increase in speed reproduction has been described by way of examples. However, the pattern signal generating circuit 15 is capable of giving not only the pattern signal described but also other pattern signals for controlling the heads 2A and 2B in manners suited for different reproducing speeds other than a speed increased by 1.5 times.
The pattern signal thus produced from the pattern signal generating circuit 15 is supplied to the conversion element driving circuit 16. The driving circuit 16 then drives the piezoelectric conversion elements 3A and 3B bringing the heads 2A and 2B to the track to be reproduced.
The conventional apparatus is thus arranged as above to produce a noiseless reproduced video signal at an arbitrary reproducing speed by obtaining the pattern signal for driving the shifting means to shift the piezoelectric conversion elements 3A, 3B, or the like. In actuality, however, the outputs of the counters 29, 20 and 22 shown in FIGS. 3(c), 3(e) and 3(f) deviate from the linear forms shown. Wave forms close to those shown in FIGS. 3(c), etc. could be obtained if the number of pulses of the capstan FG signal per unit time is infinitely great and the oscillating frequency of the oscillator 27 is extremely high. However, the number of pulses of the capstan FG signal actually generated per unit field (or a period during which the record bearing medium is shifted an extent corresponding to one TP) is limited to a number between several to ten odd by arrangement of the capstan 10 resulting from efforts exerted to reduce the size of the apparatus and to increase recording density. Accordingly, the actual outputs of the counters 20 and 22 include small stepwise variations. In the event of a mode in which the record bearing medium moving speed is low, such as a speed used for slow motion reproduction in particular, the number of pulses of the capstan FG signal generated per unit time is extremely small and thus may be counted only two or three times per turn of the rotary head.
FIGS. 5(a) to 5(g) show in a timing chart the actual output wave forms of the various parts of FIG. 2. This timing chart also shows the operation for a 1.5 times increase in speed reproduction. In this instance, four pulses of the capstan FG signal are obtained with the magnetic tape, moved an extent corresponding to one interval of the CTL signal. In other words, the frequency of the capstan FG signal to be supplied to the input terminal 17 is 180 Hz. Furthermore, for the sake of a simplified illustration, the timing chart is based on the assumption that the oscillation frequency of the oscillator 27 is 180 Hz and that the phase of the capstan FG signal and that of the output of the oscillator 27 are in synchronization with each other.
As is apparent from FIGS. 5(a) to 5(g), the driving pattern signal changes stepwise. Generally, the conversion element driving circuit 16 includes a low-pass filter (hereinafter called LPF), which filters the signal produced from the adder 25. Therefore, a certain degree of such stepwise changes can be somewhat corrected through the filter LPF. However, in cases where the number of pulses of the capstan FG signal generated per unit time is very small, as mentioned above, the stepwise changes inevitably remain in the driving pattern signal. In such a case, it becomes almost impossible to accurately trace the recording tracks. Also, the stepwise changes have caused a ringing of the shifting means such as the piezoelectric conversion elements 3A, 3B, or the like, to hinder adequate tracing of the heads 2A, 2B. To prevent this, it is conceivable to arrange an extensively low cut-off frequency of the filter LPF of the conversion element driving circuit 16. In that instance, however, the shape of the driving pattern signal will deviate greatly from the ideal shape of the pattern signal as shown in FIG. 3. Its phase also deviates greatly from the original phase.
Furthermore, in driving the rotary head shifting means with the above-stated driving pattern signal, the positional deviation which is called tracking deviation and which generally arises between the recording track and the rotary head 2A, 2B during normal reproduction (made at the same tape speed as the tape speed used for recording) also arises in that case. In the conventional VTR of the type mentioned above, the reproduced CTL signal is used for correction of a tracking error (hereinafter simply called tracking). However, this method requires a period of time for having the magnetic tape 1 travel at least one frame before such a correction can be effected and, thus, has been incapable of instantly performing tracking. In the event of slow motion reproduction in particular, the intervals at which the reproduced CTL signal is obtainable become long as the tape 1 is moved at a low speed. Therefore, an extremely long period of time has been required for tracking.
Meanwhile, as a result of reduction in size of VTR's during recent years, there have been proposed VTR's of the kind wherein, instead of recording the CTL signal, pilot signals of different frequencies are respectively recorded on recording tracks; and tracking is carried out with a tracking control signal (hereinafter called an ATF signal) obtained by reproducing these pilot signals. In the VTR of this kind, however, in carrying out varied speed reproductions with the shifting means as described above, tracking is uncontrollable until the reproducing head 2A, 2B actually traces the track because there is no CTL signal provided. Therefore, although the center line of the recording track and the tracing locus of the reproducing rotary head 2A, 2B are parallel with each other, they deviate from each other in the direction of travel of the medium at the initial stage of the varied speed reproduction.
Generally, the capstan 10 is controlled by means of the ATF signal after commencement of tracing. However, a certain length of time is necessary for following the recording track. To solve this problem, therefore, the ATF signal may conceivably be added to the driving pattern signal in the event of varied speed reproduction. However, the ATF signal cannot be obtained until the reproducing rotary head 2A, 2B begins to trace the tape 1. In a case where the tracing locus of the reproducing head 2A, 2B is always deviating in the fixed direction from the recording track as mentioned above, tracking must be performed every time a track is traced and thus the shifting means is driven with the ATF signal immediately after tracing commences. In this manner, stable operation of the shifting means is hardly possible. Besides, since tracking is not performed at the beginning of tracing, a reproduced image thus obtained deteriorates.
It is an object of this invention to provide a rotary head type reproducing apparatus which is capable of solving some of or all of the above-stated problems.
It is another object of the invention to provide a rotary head type reproducing apparatus wherein there is provided shifting means for shifting the rotary head in a direction which crosses the rotating plane thereof with a control signal which is in close proximity to an ideal analogously varying control signal, so that recording tracks can be accurately traced without increasing the precision of the structural arrangement of moving means, including the capstan 10, etc.
It is a further object of this invention to provide a rotary head type reproducing apparatus which is capable of performing stable and quick tracking, regardless of the moving speed of the record bearing medium with the shifting means shifting the rotary head in a direction which crosses the rotating plane thereof.
These and further objects and features of the invention will become apparent from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.